A. Field of the Invention
The present invention relates to electronic telephone station apparatus and more particularly to a telephone instrument which is capable of signalling in both the dial pulse and DTMF (Dual Tone Multifrequency) tone signalling modes either manually or automatically to transmit various combinations of dial pulse digits and tode sequences.
B. Description of the Prior Art
Telephone station apparatus of the type shown, for example, in U.S. Pat. No. 3,932,709 which issued to D. G. Hoff, et al on Jan. 13, 1976, and U.S. Pat. No. 3,760,121 which issued to S. Nissim of Sept. 18, 1973, provide normal telephone communications, display various keyed-in digits from a key board array and arithmetic results of an interconnected calculator, and include provisions for the output signalling of stored digits.
The apparatus described in the aforementioned U.S. Pat. No. 3,760,121 utilized a frequency divider a decoder stage and a conventional multifrequency oscillator circuit to provide DTMF tone signalling from received BCD format signals from a high frequency display control stage and an assembling-storage stage.
A mixed dialing module is provided in the apparatus of the aforementioned U.S. Pat. No. 3,932,709 to permit tone or pulse dialing from a common keypad whereby tone dialing phones are automatically switched to rotary dialing whenever an internal "com-line", for example, is selected. The apparatus is useful to avoid total conversion of all instruments to tone dialing within a PABX network or a network where a majority of phones are of the rotary dial type, internal "com-lines" are used and a miniority of phones are to be provided with tone dialing capability for outside lines. A dial tone detector is provided to dial through an access code or codes when using a stored number dialer. The mixed dialing module is controlled by detecting the current flow at the line selector of "com-lines" due to relocated "A-1" leads. The apparatus therefore completes a call in either the rotary dial or the tone dialing mode. Function keys other than those in the normal pushbutton array are utilized such as a PM button (phone memory) and an RM button (recalls memory) wherein the PM button is effective to store a number, the RM button is effective to display the stored number and a DIAL BUTTON is utilized to place the call.
Although the telephone station apparatus of the prior art are generally satisfactory to accomplish their intended purpose, they are not generally suited to accomplish both dial pulse and DTMF tone signalling within a single signalling sequence and in either a manual or automatic mode under the control of the operator.